The present invention claims priority from Japanese Patent Application No. 10-120848 filed Apr. 30, 1998, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to the structure of a semiconductor light-receiving element capable of transmitting laser light, and to a manufacturing method thereof. Semiconductor light-receiving elements capable of transmitting laser light can be utilized as sensors for the alignment of precision machine tools and electron microscopes.
2. Description of Related Art
On a precision machine tool it is necessary to align a plurality of components with an accuracy of 1 xcexcm over a distance of several meters. Laboratory equipment involving lasers also requires the same degree of accuracy in the alignment of optical axes. A laser diode is used as the light source for such alignment, and semiconductor light-receiving elements such as photodiodes are used as optical sensors for receiving the laser light emitted by this laser diode. There are known techniques of using photodiodes in combination with a laser diode.
FIG. 1 shows an example of an alignment of components by means of a reference beam of laser light. In this example, photodiodes are used as the semiconductor light-receiving elements. As shown in FIG. 1, light source 40 is disposed parallel to, and at one end of, components 50, 51 and 52 requiring alignment, and emits laser light with a small spot size. This laser light is received using semiconductor devices 30, 31 and 32. These semiconductor devices are mechanically mounted on components 50, 51 and 52, and have photodiodes with extremely small light-receiving areas. A known structure for such semiconductor devices 30, 31 and 32 comprises a plurality of photodiodes formed on a single light-receiving surface. By identifying which of these photodiodes receives the laser light, the alignment can be automatically adjusted.
In such prior art, when semiconductor device 30 is disposed as a light-receiving sensor on the single optical axis, the laser light will be interrupted by this semiconductor device. If it is necessary to align a multiplicity of components 50, 51 and 52 disposed over a relatively long distance, then semiconductor devices 30, 31 and 32 will have to be used and adjusted one by one, starting from the semiconductor device nearest light source 40. When the position adjustment has been completed for a given semiconductor device, it has to be removed from the optical axis so that the next component can be aligned. This complicates the alignment operation and makes it necessary to repeat the operation. Further, it is impossible to confirm as a whole that all components 50, 51 and 52 have been correctly adjusted.
FIG. 2 shows an example of the alignment of components using a reference beam of laser light, and beam splitters in order to overcome the problems noted above. In the example shown in FIG. 2, beam splitters 20, 21 and 22, which may be semitransparent mirrors or prisms, are respectively mounted on components 50, 51 and 52, and the optical axes branched off by these beam splitters are aligned by receiving light by means of semiconductor devices 30, 31 and 32. FIG. 3 shows the relation between a beam splitter and a semiconductor device. However, in the example of FIG. 2, the optical system is complicated and the optical axes of beam splitters 20, 21 and 22 are not exactly co-linear, resulting in noise being produced in the beam wavefront. Moreover, after the beam is propagated over a long distance, spot shape and beam spreading can become distorted.
If the semiconductor device used as a light-receiving sensor is transparent so that the laser light which one semiconductor device utilizes for the alignment of a component can be transmitted without further contrivance, and other semiconductor devices are able to utilize this laser light for the alignment of other components, then problems of the sort described above can be solved.
The present invention has been created in view of this technical background. It is an object of this invention to provide a semiconductor light-receiving element with a structure which absorbs only some of the received light beam and which allows the greater part to be transmitted to its rear face. It is a further object of this invention to simplify the operation of mechanically aligning components on an optical axis. It is yet another object of this invention to provide a device which, when a multiplicity of components are to be aligned, enables the alignment of all the components to be confirmed as a whole.
According to a first aspect, this invention is a semiconductor light-receiving element formed on part of a semiconductor bulk as a diaphragm which is sufficiently thin to allow the transmission of laser light.
Because this enables laser light which has been transmitted through one semiconductor light-receiving element to reach another semiconductor light-receiving element, it is for example possible to adjust the alignment of a plurality of components by using laser light with a single optical axis as a common reference beam. The alignment operation can therefore be simplified, and when a multiplicity of components are to be aligned, the alignment of all the components as a whole can be confirmed.
According to a second aspect, this invention is directed to a semiconductor device including a plurality of the aforesaid semiconductor light-receiving elements formed in extremely close proximity on a single semiconductor bulk. A separate electrode is provided on each of these semiconductor light-receiving elements.
If the semiconductor device has two light receiving elements, the position at which a laser spot hits the semiconductor device can be detected in one dimension by for example shining a laser spot, which constitutes a single point, on the semiconductor device and measuring the difference in the photocurrents generated by these two semiconductor light-receiving elements.
An alternative configuration is possible. Namely, if the semiconductor device has four light receiving elements, the four semiconductor light-receiving elements are disposed in respective quadrants demarcated by imaginary orthogonal X and Y axes on the aforesaid diaphragm. By disposing the semiconductor light-receiving elements in this manner, the position at which a laser spot hits the semiconductor device can be detected in two dimensions by for example shining a laser spot, which constitutes a single point, on the semiconductor device and measuring the differences in the photocurrents generated by these four semiconductor light-receiving elements.
According to a third aspect, this invention is directed to a manufacturing method for a transparent semiconductor light-receiving element. The manufacturing method includes etching a silicon substrate of one conduction type from its rear face until it is sufficiently thin to allow transmission of laser light, doping the etched portion from the front face with a dopant of the opposite conduction type, and forming an electrode for the electrical connection on this doped portion.
According to a fourth aspect, this invention is directed to a semiconductor light-receiving element which is different from the aforesaid semiconductor light-receiving element formed as a diaphragm, wherein the equivalent of a transparent semiconductor light-receiving element can be formed by providing a passage or passages as a lattice-like structure. Light can pass through the passage(s) from the front to the rear face of a semiconductor bulk. The passage(s) is (are) provided in a region which includes a light-receiving part which has been formed on part of the front face of the semiconductor bulk.
A semiconductor light-receiving element formed in this manner can be used in the same way as the aforesaid semiconductor light-receiving element formed as a diaphragm. Namely, it can be applied to a semiconductor device, a plurality of the semiconductor light-receiving elements can be formed in extremely close proximity on a single semiconductor bulk, a separate electrode can be provided on each of these semiconductor light-receiving elements, a passage or passages through which light can pass can be formed as a lattice-like structure, and the number of light receiving elements can be 2 or 4.
An alternative configuration is as follows. Namely, if the number of light receiving objects is 4, the four semiconductor light-receiving elements are disposed in respective quadrants demarcated by imaginary orthogonal X and Y axes on the aforesaid diaphragm.